The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
A vibration module comprising a pair of piezoelectric actuating elements located on the steering wheel is known from EP 0 856 432 A2. However, practically suitable piezoelectric actuating elements require very high operating currents. Furthermore, because the forces used to rotate the steering wheel usually act on the piezoelectric elements these have to be largely dimensioned.
From another embodiment of EP 0 856 432 A2 a vibration module comprising an electric motor with an eccentric mass connected to the motor axis is known. A significant portion of the vibrations exerted by the rotating eccentric mass have components perpendicular to the steering rim plane. These vibrations effectively generate unwanted noise in the steering wheel column and adjacent components such as the instrument panel and/or a central arm rest. Furthermore, since a significant portion of the vibration energy is transmitted away through the steering wheel column, the strength of the vibrations in the steering rim and therefore the effectiveness of the alert function is reduced.
It remains desirable to provide a driver alert system with a compact and effective vibration module and with reduced noise in the steering wheel column and adjacent components.